Gas turbines are widely used in industrial and commercial operations. A typical gas turbine includes a compressor at the front, one or more combustors around the middle, and a turbine at the rear. The compressor imparts kinetic energy to the working fluid (e.g., air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows to the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine where they expand to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The compressor and the turbine typically share a common rotor which extends from near the front of the compressor to near the rear of the turbine. The rotor typically is configured to direct a portion of the compressed air through one or more cooling circuits to cool various components of the gas turbine. The cooling circuits, however, may not be capable of adequately cooling and/or purging an aft joint of a last stage wheel without creating a large temperature gradient in the last stage wheel.